Non-polar (Al,B,In,Ga)N quantum well and heterostructure materials and devices

ABSTRACT

A method for forming non-polar (Al,B,In,Ga)N quantum well and heterostructure materials and devices. Non-polar (11  2 0) a-plane GaN layers are grown on an r-plane (1  1 02) sapphire substrate using MOCVD. These non-polar (11  2 0) a-plane GaN layers comprise templates for producing non-polar (Al,B,In,Ga)N quantum well and heterostructure materials and devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. Section 120 ofco-pending and commonly-assigned U.S. Utility patent application Ser.No. 11/472,033, filed on Jun. 21, 2006, by Michael D. Craven, StaciaKeller, Steven P. DenBaars, Tal Margalith, James S. Speck, ShujiNakamura, and Umesh K. Mishra, entitled “NON-POLAR (Al,B,In,Ga)N QUANTUMWELL AND HETEROSTRUCTURE MATERIALS AND DEVICES, which application is adivisional application claiming the benefit under 35 U.S.C. Section 120and Section 121 of U.S. Utility patent application Ser. No. 10/413,690,filed on Apr. 15, 2003, now U.S. Pat. No. 7,091,514, issued Aug. 15,2006, by Michael D. Craven, Stacia Keller, Steven P. DenBaars, TalMargalith, James S. Speck, Shuji Nakamura, and Umesh K. Mishra, entitled“NON-POLAR (Al,B,In,Ga)N QUANTUM WELL AND HETEROSTRUCTURE MATERIALS ANDDEVICES which application claims the benefit under 35 U.S.C. §119(e) ofthe following co-pending and commonly-assigned U.S. Provisional PatentApplication Ser. No. 60/372,909, entitled “NON-POLAR GALLIUM NITRIDEBASED THIN FILMS AND HETEROSTRUCTURE MATERIALS,” filed on Apr. 15, 2002,by Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margalith,James S. Speck, Shuji Nakamura, and Umesh K. Mishra,

all of which applications are incorporated by reference herein.

This application is related to the following co-pending andcommonly-assigned United States Utility patent applications:

Ser. No. 10/413,691, entitled “NON-POLAR A-PLANE GALLIUM NITRIDE THINFILMS GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION,” filed Apr. 15,2003, by Michael D. Craven and James S. Speck, and

Ser. No. 10/413,913, entitled “DISLOCATION REDUCTION IN NON-POLARGALLIUM NITRIDE THIN FILMS,” Apr. 15, 2003, now issued U.S. Pat. No.6,900,070 issued May 31, 2005, by Michael D. Craven, Stacia Keller,Steven P. DenBaars, Tal Margalith, James S. Speck, Shuji Nakamura, andUmesh K. Mishra,

both of which applications are incorporated by reference herein.

FIELD OF THE INVENTION

The invention is related to semiconductor materials, methods, anddevices, and more particularly, to non-polar (Al,B,In,Ga)N quantum welland heterostructure materials and devices.

DESCRIPTION OF THE RELATED ART

(Note: This application references a number of different patents,applications and/or publications as indicated throughout thespecification by one or more reference numbers. A list of thesedifferent publications ordered according to these reference numbers canbe found below in the section entitled “References.” Each of thesepublications is incorporated by reference herein.)

Current state of the art (Al,B,In,Ga)N heterostructures and quantum wellstructures employ c-plane (0001) layers. The total polarization of aIII-N film consists of spontaneous and piezoelectric polarizationcontributions, which both originate from the single polar [0001] axis ofthe wurtzite nitride crystal structure. Polarization discontinuitieswhich exist at surfaces and interfaces within nitride heterostructuresare associated with fixed sheet charges, which in turn produce electricfields. Since the alignment of these internal electric fields coincideswith the growth direction of the c-plane (0001) layers, the fieldsaffect the energy bands of device structures.

In quantum wells, the “tilted” energy bands spatially separate electronsand hole wave functions, which reduces the oscillator strength ofradiative transitions and red-shifts the emission wavelength. Theseeffects are manifestations of the quantum confined Stark effect (QCSE)and have been thoroughly analyzed for GaN/(Al,Ga)N quantum wells. SeeReferences 1-8. Additionally, the large polarization-induced fields arepartially screened by dopants and impurities, so the emissioncharacteristics can be difficult to engineer accurately.

The internal fields are also responsible for large mobile sheet chargedensities in nitride-based transistor heterostructures. Although theselarge 2 D electron gases (2 DEGs) are attractive and useful for devices,the polarization-induced fields, and the 2 DEG itself, are difficult tocontrol accurately.

Non-polar growth is a promising means of circumventing the strongpolarization-induced electric fields that exist in wurtzite nitridesemiconductors. Polarization-induced electric fields do not affectwurtzite nitride semiconductors grown in non-polar directions (i.e.,perpendicular to the [0001] axis) due to the absence of polarizationdiscontinuities along non-polar growth directions.

Recently, two groups have grown non-polar GaN/(Al,Ga)N multiple quantumwells (MQWs) via molecular beam epitaxy (MBE) without the presence ofpolarization-induced electric fields along non-polar growth directions.Waltereit et al. grew m-plane GaN/Al_(0.1)Ga_(0.9)N MQWs on γ-LiAlO₂(100) substrates and Ng grew a-plane GaN/Al_(0.15)Ga_(0.85)N MQW onr-plane sapphire substrates. See References 9-10.

Despite these results, the growth of non-polar GaN orientations remainsdifficult to achieve in a reproducible manner.

SUMMARY OF THE INVENTION

The present invention describes a method for forming non-polar(Al,B,In,Ga)N quantum well and heterostructure materials and devices.First, non-polar (11 20) a-plane GaN thin films are grown on a (1 102)r-plane sapphire substrate using metalorganic chemical vapor deposition(MOCVD). These non-polar (11 20) a-plane GaN thin films are templatesfor producing non-polar (Al,B,In,Ga)N quantum well and heterostructurematerials and devices thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a flowchart that illustrates the steps of a method for formingnon-polar (Al,B,In,Ga)N quantum well and heterostructure materials anddevices according to a preferred embodiment of the present invention;

FIG. 2 illustrates the photoluminescence (PL) spectra of 5-perioda-plane In_(0.1)GaN/In_(0.03)GaN MQW structures with nominal well widthsof 1.5 nm, 2.5 nm, and 5.0 nm measured at room temperature;

FIG. 3 illustrates the PL spectra of an a-planeIn_(0.03)Ga_(0.97)N/In_(0.1)Ga_(0.9)N MQW structure with a nominal wellwidth of 5.0 nm measured for various pump powers;

FIG. 4( a) shows a 2θ-ω x-ray diffraction scan of the 10-periodAl_(0.4)Ga_(0.6)N/GaN superlattice, which reveals clearly definedsatellite peaks;

FIG. 4( b) illustrates the PL spectra of the superlattice characterizedin FIG. 4( a);

FIG. 5( a) shows a 2θ-ω diffraction scan that identifies the growthdirection of the GaN film as (11 20) a-plane GaN;

FIG. 5( b) is a compilation of off-axis φ scans used to determine thein-plane epitaxial relationship between GaN and r-sapphire, wherein theangle of inclination ψ used to access the off-axis reflections is notedfor each scan;

FIG. 5( c) is a schematic illustration of the epitaxial relationshipbetween the GaN and r-plane sapphire;

FIGS. 6( a) and 6(b) are cross-sectional and plan-view transmissionelectron microscopy (TEM) images, respectively, of the defect structureof the a-plane GaN films on r-plane sapphire; and

FIGS. 7( a) and 7(b) are atomic force microscopy (AFM) amplitude andheight images, respectively, of the surface of the as-grown a-plane GaNfilms.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

The purpose of the present invention is to provide a method forproducing non-polar (Al,B,In,Ga)N quantum well and heterostructurematerials and devices, using non-polar (11 20) a-plane GaN thin films astemplates.

The growth of device-quality non-polar (11 20) a-plane GaN thin films on(1 102) r-plane sapphire substrates via MOCVD is described in co-pendingand commonly-assigned U.S. Provisional Patent Application Ser. No.60/372,909, entitled “NON-POLAR GALLIUM NITRIDE BASED THIN FILMS ANDHETEROSTRUCTURE MATERIALS,” filed on Apr. 15, 2002, by Michael D.Craven, Stacia Keller, Steven P. DenBaars, Tal Margalith, James S.Speck, Shuji Nakamura, and Umesh K. Mishra, as well as co-pending andcommonly-assigned U.S. Utility patent application Ser. No. 10/413,691,entitled “NON-POLAR A-PLANE GALLIUM NITRIDE THIN FILMS GROWN BYMETALORGANIC CHEMICAL VAPOR DEPOSITION,” filed on same date herewith, byMichael D. Craven and James S. Speck, both of which applications areincorporated by reference herein.

The present invention focuses on the subsequent growth of (Al,B,In,Ga)Nquantum wells and heterostructures on the (11 20) a-plane GaN layers.The luminescence characteristics of these structures indicate thatpolarization-induced electric fields do not affect their electronic bandstructure, and consequently, polarization-free structures have beenattained. The development of non-polar (Al,B,In,Ga)N quantum wells andheterostructures is important to the realization of high-performance(Al,B,In,Ga)N-based devices which are unaffected by polarization-inducedelectric fields.

Potential devices to be deposited on non-polar (11 20) a-plane GaNlayers include laser diodes (LDs), light emitting diodes (LEDs),resonant cavity LEDs (RC-LEDs), vertical cavity surface emitting lasers(VCSELs), high electron mobility transistors (HEMTs), heterojunctionbipolar transistors (HBTs), heterojunction field effect transistors(HFETs), as well as UV and near-UV photodetectors.

Process Steps

FIG. 1 is a flowchart that illustrates the steps of a method for formingnon-polar (Al,B,In,Ga)N quantum well and heterostructure materials anddevices according to a preferred embodiment of the present invention.The steps of this method include the growth of “template” (11 20)a-plane GaN layers, followed by the growth of layers with differingalloy compositions for quantum wells and heterostructures.

Block 100 represents loading of a sapphire substrate into a vertical,close-spaced, rotating disk, MOCVD reactor. For this step, epi-readysapphire substrates with surfaces crystallographically oriented within+/−2° of the sapphire r-plane (1 120) may be obtained from commercialvendors. No ex-situ preparations need be performed prior to loading thesapphire substrate into the MOCVD reactor, although ex-situ cleaning ofthe sapphire substrate could be used as a precautionary measure.

Block 102 represents annealing the sapphire substrate in-situ at a hightemperature (>1000° C.), which improves the quality of the substratesurface on the atomic scale. After annealing, the substrate temperatureis reduced for the subsequent low temperature nucleation layerdeposition.

Block 104 represents depositing a thin, low temperature, low pressure,nitride-based nucleation layer as a buffer layer on the sapphiresubstrate. Such layers are commonly used in the heteroepitaxial growthof c-plane (0001) nitride semiconductors. In the preferred embodiment,the nucleation layer is comprised of, but is not limited to, 1-100nanometers (nm) of GaN deposited at approximately 400-900° C. and 1 atm.

After depositing the nucleation layer, the reactor temperature is raisedto a high temperature, and Block 106 represents growing the epitaxial(11 20) a-plane GaN layers to a thickness of approximately 1.5 μn. Thehigh temperature growth conditions include, but are not limited to,approximately 1100° C. growth temperature, 0.2 atm or less growthpressure, 30 μmol per minute Ga flow, and 40,000 μmol per minute N flow,thereby providing a V/III ratio of approximately 1300). In the preferredembodiment, the precursors used as the group III and group V sources aretrimethylgallium and ammonia, respectively, although alternativeprecursors could be used as well. In addition, growth conditions may bevaried to produce different growth rates, e.g., between 5 and 9 Å persecond, without departing from the scope of the present invention.

Upon completion of the high temperature growth step, Block 108represents cooling the epitaxial (11 20) a-plane GaN layers down under anitrogen overpressure.

Finally, Block 110 represents non-polar (Al,B,In,Ga)N layers, withdiffering alloy compositions and hence differing electrical properties,being grown on the non-polar (11 20) a-plane GaN layers. These non-polar(Al,B,In,Ga)N layers are used to produce quantum wells andheterostructures.

The quantum wells employ alternating layers of different bandgap suchthat “wells” are formed in the structure's energy band profile. Theprecise number of layers in the structure depends on the number ofquantum wells desired. Upon excitation, electrons and holes accumulatein the wells of the conduction and valence bands, respectively.Band-to-band recombination occurs in the well layers since thedensity-of-states is highest at these locations. Thus, quantum wells canbe engineered according to the desired emission characteristics andavailable epitaxial growth capabilities.

The nominal thickness and composition of the layers successfully grownon the non-polar (11 20) a-plane GaN layers include, but are not limitedto:

8 nm Si-doped In_(0.03)GaN barrier

1.5, 2.5, or 5 nm In_(0.1)GaN well

Moreover, the above Blocks may be repeated as necessary. In one example,Block 110 was repeated 5 times to form an MQW structure that was cappedwith GaN to maintain the integrity of the (In,Ga)N layers. In thisexample, the layers comprising the MQW structure were grown via MOCVD ata temperature of 825° C. and atmospheric pressure.

The luminescence characteristics of this structure indicate thatpolarization-induced electric fields do not affect the band profiles,and the quantum wells can be considered polarization-free. For example,FIG. 2 illustrates the photoluminescence (PL) spectra of 5-perioda-plane In_(0.1)GaN/In_(0.03)GaN MQW structures with nominal well widthsof 1.5 nm, 2.5 nm, and 5.0 nm measured at room temperature. The peak PLemission wavelength and intensity increase with increasing well width.

Further, FIG. 3 illustrates the PL spectra of an a-planeIn_(0.03)Ga_(0.97)N/In_(0.1)Ga_(0.9)N MQW structure with a nominal wellwidth of 5.0 nm measured for various pump powers. PL intensity increaseswith pump power as expected while the peak emission wavelength is pumppower independent, indicating that the band profiles are not influencedby polarization-induced electric fields.

In addition to (In,Ga)N quantum wells, heterostructures containing(Al,Ga)N/GaN superlattices may also be grown on the non-polar (11 20)a-plane GaN layers. For example, heterostructures typically consist oftwo layers, most commonly (AlGa)N on GaN, to produce an electricalchannel necessary for transistor operation. The thickness andcomposition of the superlattice layers may comprise, but are not limitedto:

9 nm Al_(0.4)GaN barrier

11 nm GaN well

In one example, Block 110 was repeated 10 times to form a 10-periodAl_(0.4)Ga_(0.6)N/GaN superlattice that was terminated with a 11 nm GaNwell layer. The superlattice was grown via MOCVD at conditions similarto those employed for the underlying template layer: ˜1100° C. growthtemperature, ˜0.1 atm growth pressure, 38 μmol/min Al flow, 20 μmol/minGa flow, and 40,000 μmol/min N flow. The Al flow was simply turned offto form the GaN well layers. Successful growth conditions are notstrictly defined by the values presented above. Similar to the (In,Ga)Nquantum wells, the luminescence characteristics of the superlatticedescribed above indicate that polarization fields do not affect thestructure.

FIG. 4( a) shows a 2θ-ω x-ray diffraction scan of the 10-periodAl_(0.4)Ga_(0.6)N/GaN superlattice, which reveals clearly definedsatellite peaks, while FIG. 4( b) illustrates the PL spectra of thesuperlattice characterized in FIG. 4( a). The absence ofpolarization-induced fields was evidenced by the 3.45 eV (˜360 nm) bandedge emission of the superlattice. The band edge emission did notexperience the subtle red-shift present in c-plane superlattices.

Experimental Results for as-Grown GaN

The crystallographic orientation and structural quality of the as-grownGaN films and r-plane sapphire were determined using a Philips™four-circle, high-resolution, x-ray diffractometer (HR-XRD) operating inreceiving slit mode with four bounce Ge(220)-monochromated Cu Kαradiation and a 1.2 mm slit on the detector arm. Convergent beamelectron diffraction (CBED) was used to determine the polarity of thea-GaN films with respect to the sapphire substrate. Plan-view andcross-section transmission electron microscopy (TEM) samples, preparedby wedge polishing and ion milling, were analyzed to define the defectstructure of a-GaN. A Digital Instruments D3000 Atomic Force Microscope(AFM) in tapping mode produced images of the surface morphology.

FIG. 5( a) shows a 2θ-ω diffraction scan that identifies the growthdirection of the GaN film as (11 20) a-plane GaN. The scan detectedsapphire (1 102), (2 204), and GaN (11 20) reflections. Within thesensitivity of these measurements, no GaN (0002) reflectionscorresponding to 2θ=34.604° were detected, indicating that there is noc-plane (0002) content present in these films, and thus instabilities inthe GaN growth orientation are not a concern.

FIG. 5( b) is a compilation of off-axis φ scans used to determine thein-plane epitaxial relationship between GaN and r-sapphire, wherein theangle of inclination ψ used to access the off-axis reflections is notedfor each scan. Having confirmed the a-plane growth surface, off-axisdiffraction peaks were used to determine the in-epitaxial relationshipbetween the GaN and the r-sapphire. Two sample rotations φ and ψ wereadjusted in order to bring off-axis reflections into the scatteringplane of the diffractometer, wherein φ is the angle of rotation aboutthe sample surface normal and ψ is the angle of sample tilt about theaxis formed by the intersection of the Bragg and scattering planes.After tilting the sample to the correct ψ for a particular off-axisreflection, φ scans detected GaN (10 10), (10 11), and sapphire (0006)peaks, as shown in FIG. 2( b). The correlation between the φ positionsof these peaks determined the following epitaxial relationship:[0001]_(GaN)∥[ 1101]_(sapphire) and [ 1100]_(GaN)∥[11 20]_(sapphire).

FIG. 5( c) is a schematic illustration of the epitaxial relationshipbetween the GaN and r-plane sapphire. To complement the x-ray analysisof the crystallographic orientation, the a-GaN polarity was determinedusing CBED. The polarity's sign is defined by the direction of the polarGa—N bonds aligned along the GaN c-axis; the positive c-axis [0001]points from a gallium atom to a nitrogen atom. Consequently, agallium-face c-GaN film has a [0001] growth direction, while anitrogen-face c-GaN crystal has a [000 1] growth direction. For a-GaNgrown on r-sapphire, [0001]_(GaN) is aligned with the sapphire c-axisprojection [ 1101]_(sapphire), and therefore, the epitaxialrelationships defined above are accurate in terms of polarity.Consequently, the positive GaN c-axis points in same direction as thesapphire c-axis projection on the growth surface (as determined viaCBED). This relationship concurs with the epitaxial relationshipspreviously reported by groups using a variety of growth techniques. SeeReferences 17, 18 and 19. Therefore, the epitaxial relationship isspecifically defined for the growth of GaN on an r-plane sapphiresubstrate.

FIGS. 6( a) and 6(b) are cross-sectional and plan-view TEM images,respectively, of the defect structure of the a-plane GaN films on anr-plane sapphire substrate. These images reveal the presence of line andplanar defects, respectively. The diffraction conditions for FIGS. 3( a)and 3(b) are g=0002 and g=10 10, respectively.

The cross-sectional TEM image in FIG. 6( a) reveals a large density ofthreading dislocations (TD's) originating at the sapphire/GaN interfacewith line directions parallel to the growth direction [11 20]. The TDdensity, determined by plan view TEM, was 2.6×10¹⁰ cm⁻². With the TDline direction parallel to the growth direction, pure screw dislocationswill have Burgers vectors aligned along the growth direction b=±[11 20])while pure edge dislocations will have b=±[0001]. The reduced symmetryof the a-GaN surface with respect to c-GaN complicates thecharacterization of mixed dislocations since the crystallographicallyequivalent [11 20] directions cannot be treated as the family <11 20>.Specifically, the possible Burgers vectors of mixed dislocations can bedivided into three subdivisions: (1) b=±[1 210] b= and (3) b=±[ 2110],(2) b=±[11 20]±[0001], and (3) b =±[11 20]±[1 210] and b=±[11 20]±[2110].

In addition to line defects, the plan view TEM image in FIG. 6( b)reveals the planar defects observed in the a-GaN films. Stacking faultsaligned perpendicular to the c-axis with a density of 3.8×10⁵ cm⁻¹ wereobserved in the plan-view TEM images. The stacking faults, commonlyassociated with epitaxial growth of close-packed planes, most likelyoriginate on the c-plane sidewalls of three-dimensional (3D) islandsthat form during the initial stages of the high temperature growth.Consequently, the stacking faults are currently assumed to be intrinsicand terminated by Shockley partial dislocations of opposite sign.Stacking faults with similar characteristics were observed in a-planeAlN films grown on r-plane sapphire substrates. See Reference 20. Thestacking faults have a common faulting plane parallel to theclose-packed (0001) and a density of ˜3.8×10⁵ cm⁻¹.

Omega rocking curves were measured for both the GaN on-axis (11 20) andoff-axis (10 11) reflections to characterize the a-plane GaN crystalquality. The full-width half-maximum (FWHM) of the on-axis peak was0.29° (1037″), while the off-axis peak exhibited a larger orientationalspread with a FWHM of 0.46° (1659″). The large FWHM values are expectedsince the microstructure contains a substantial dislocation density.According to the analysis presented by Heying et al. for c-GaN films onc-sapphire, on-axis peak widths are broadened by screw and mixeddislocations, while off-axis widths are broadened by edge-component TD's(assuming the TD line is parallel to the film normal). See Reference 21.A relatively large edge dislocation density is expected for a-GaN onr-sapphire due to the broadening of the off-axis peak compared to theon-axis peak. Additional microstructural analyses are required tocorrelate a-GaN TD geometry to rocking curve measurements.

FIGS. 7( a) and 7(b) are AFM amplitude and height images, respectively,of the surface of the as-grown a-plane GaN film. The surface pits in theAFM amplitude image of FIG. 7( a) are uniformly aligned parallel to theGaN c-axis, while the terraces visible in the AFM height image of FIG.7( b) are aligned perpendicular to the c-axis.

Although optically specular with a surface RMS roughness of 2.6 nm, thea-GaN growth surface is pitted on a sub-micron scale, as can be clearlyobserved in the AFM amplitude image shown in FIG. 7( a). It has beenproposed that the surface pits are decorating dislocation terminationswith the surface; the dislocation density determined by plan view TEMcorrelates with the surface pit density within an order of magnitude.

In addition to small surface pits aligned along GaN c-axis [0001], theAFM height image in FIG. 7( b) reveals faint terraces perpendicular tothe c-axis. Although the seams are not clearly defined atomic steps,these crystallographic features could be the early signs of the surfacegrowth mode. At this early point in the development of the a-planegrowth process, neither the pits nor the terraces have been correlatedto particular defect structures.

References

The following references are incorporated by reference herein:

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Conclusion

This concludes the description of the preferred embodiment of thepresent invention. The following describes some alternative embodimentsfor accomplishing the present invention.

For example, variations in non-polar (Al,In,Ga)N quantum wells andheterostructures design and MOCVD growth conditions may be used inalternative embodiments. Moreover, the specific thickness andcomposition of the layers, in addition to the number of quantum wellsgrown, are variables inherent to quantum well structure design and maybe used in alternative embodiments of the present invention.

Further, the specific MOCVD growth conditions determine the dimensionsand compositions of the quantum well structure layers. In this regard,MOCVD growth conditions are reactor dependent and may vary betweenspecific reactor designs. Many variations of this process are possiblewith the variety of reactor designs currently being using in industryand academia.

Variations in conditions such as growth temperature, growth pressure,V/III ratio, precursor flows, and source materials are possible withoutdeparting from the scope of the present invention. Control of interfacequality is another important aspect of the process and is directlyrelated to the flow switching capabilities of particular reactordesigns. Continued optimization of the growth conditions will result inmore accurate compositional and thickness control of the integratedquantum well layers described above.

In addition, a number of different growth methods other than MOCVD couldbe used in the present invention. For example, the growth method couldalso be molecular beam epitaxy (MBE), liquid phase epitaxy (LPE),hydride vapor phase epitaxy (HVPE), sublimation, or plasma-enhancedchemical vapor deposition (PECVD).

Further, although non-polar a-plan GaN thin films are described herein,the same techniques are applicable to non-polar m-plane GaN thin films.Moreover, non-polar InN, AlN, and AlInGaN thin films could be createdinstead of GaN thin films.

Finally, substrates other than sapphire substrate could be employed fornon-polar GaN growth. These substrates include silicon carbide, galliumnitride, silicon, zinc oxide, boron nitride, lithium aluminate, lithiumniobate, germanium, aluminum nitride, and lithium gallate.

In summary, the present invention describes a method for formingnon-polar (Al,B,In,Ga)N quantum well and heterostructure materials anddevices. First, non-polar (11 20) a-plane GaN thin film layers are grownon a (1 102) r-plane sapphire substrate using MOCVD. These non-polar (1120) a-plane GaN layers comprise templates for producing non-polar(Al,B,In,Ga)N quantum well and heterostructure materials and devices.

The foregoing description of one or more embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

1. A nitride semiconductor device, comprising one or more non-polar (Al,B, In, Ga)N quantum well layers containing Indium, wherein at least oneof the (Al, B, In, Ga)N quantum well layers has a thickness greater than5 nanometers and emits light having a peak photoluminescence (PL)emission wavelength and an intensity that are greater than a PL emissionwavelength and an intensity of light emitted from a non-polar (Al, B,In, Ga)N quantum well layer having a thickness of 5 nanometers or less.2. The device of claim 1, wherein at least one of the (Al, B, In, Ga)Nquantum well layers is an InGaN quantum well layer.
 3. The device ofclaim 1, wherein the device is a light emitting diode or laser diode andan active layer of the light emitting diode or the laser diode includesthe one or more non-polar (Al, B, In, Ga)N quantum well layers.
 4. Thedevice of claim 1, wherein the device includes a heterostructure formedfrom the one or more non-polar (Al, B, In, Ga)N quantum well layers. 5.The device of claim 1, wherein the one or more non-polar (Al, B, In,Ga)N quantum well layers are non-polar a-plane layers.
 6. The device ofclaim 1, wherein the one or more non-polar (Al, B, In, Ga)N quantum welllayers are non-polar m-plane layers.
 7. A nitride semiconductor device,comprising one or more non-polar (Al, B, In, Ga)N layers grown on anon-polar GaN substrate wherein the non-polar (Al, B, In, Ga)N layersinclude one or more non-polar (Al, B, In, Ga)N quantum wells that has athickness greater than 5 nanometers and emits light having a peakphotoluminescence (PL) emission wavelength and an intensity that aregreater than a PL emission wavelength and an intensity of light emittedfrom a non-polar (Al, B, In, Ga)N quantum well having a thickness of 5nanometers or less.
 8. The device of claim 7, wherein at least one ofthe quantum wells is an indium containing quantum well layer.
 9. Thedevice of claim 8, wherein at least one of the quantum wells is an InGaNquantum well.
 10. The device of claim 7, wherein the non-polar (Al, B,In, Ga)N layers include a heterostructure.
 11. The device of claim 7,wherein the device is a light emitting diode or laser diode and anactive layer of the light emitting diode or the laser diode includes aheterostructure or quantum well formed from the one or more non-polar(Al, B, In, Ga)N layers.
 12. The device of claim 7, wherein the deviceincludes a heterostructure formed from the one or more non-polar (Al, B,In, Ga)N layers.
 13. The device of claim 7, wherein the one or morenon-polar (Al, B, In, Ga)N layers are non-polar a-plane layers grown onan a-plane surface of the non-polar GaN substrate.
 14. The device ofclaim 7, wherein the one or more non-polar (Al, B, In, Ga)N layers arenon-polar m-plane layers grown on an m-plane surface of the non-polarGaN substrate.
 15. The device of claim 7, wherein the non-polar GaNsubstrate has a threading dislocation density of no more than 2.6×10¹⁰cm⁻².
 16. The device of claim 7, wherein the non-polar GaN substrate hasa stacking fault density of no more than 3.8×10⁵ cm⁻¹.
 17. The device ofclaim 7, wherein the one or more non-polar (Al, B, In, Ga)N layers aregrown on a grown non-polar surface of the non-polar GaN substrate.
 18. Amethod for fabricating a nitride semiconductor device, comprising:growing one or more non-polar (Al, B, In, Ga)N quantum well layerscontaining Indium, wherein at least one of the (Al, B, In, Ga)N quantumwell layers has a thickness greater than 5 nanometers and emits lighthaving a peak photoluminescence (PL) emission wavelength and anintensity that are greater than a PL emission wavelength and anintensity of light emitted from a non-polar (Al, B, In, Ga)N quantumwell layer having a thickness of 5 nanometers or less.
 19. The method ofclaim 18, wherein the growing is by metal organic chemical vapordeposition (MOCVD).
 20. The method of claim 18, wherein the non-polar(Al, B, In, Ga)N quantum well layers are grown on or above a non-polarGaN substrate.
 21. The method of claim 18, further comprising obtaininga grown non-polar surface of GaN substrate, and growing the quantum welllayers on or above the grown non-polar surface.